Two-peak current control for flyback voltage converters

Abstract

A system including a switch configured to supply power to a load. A first comparator is configured to compare a first current through the switch to a first threshold. A second comparator is configured to compare the first current through the switch to a second threshold. The second threshold is greater than the first threshold. A current control module is configured to turn off the switch (i) for a first duration in response to the first current through the switch being greater than or equal to the first threshold and (ii) for a second duration in response to the first current through the switch being greater than or equal to the second threshold. The current control module is configured to adjust the second duration based on a difference between an estimated current through the load and a desired current through the load.

What is claimed is: 
     
       1. A system comprising:
 a switch configured to supply power to a load in response to the switch being turned on by pulse width modulation pulses; 
 a first comparator configured to compare a first current through the switch to a first threshold and generate a first output in response to the first current being greater than or equal to the first threshold; 
 a second comparator configured to compare the first current through the switch to a second threshold and generate a second output in response to the first current being greater than or equal to the second threshold, wherein the second threshold is greater than the first threshold; 
 a current estimating module configured to determine an estimated current through the load based on the first current through the switch; and 
 a current control module configured to
 select the first output or the second output, 
 turn off the switch based on the first output or the second output, and 
 
 adjust a duration for which the second output is selected based on a difference between the estimated current through the load and a desired current through the load. 
 
     
     
       2. The system of  claim 1 , wherein:
 the power is generated based on an AC voltage, and 
 the adjustment of the duration for which the second output is selected prevents variation of a second current through the load due to an imbalance in the AC voltage. 
 
     
     
       3. The system of  claim 1 , wherein:
 the power is generated based on an AC voltage having a predetermined period, and 
 the current control module is configured to reduce a total harmonic distortion in a second current through the load by limiting the duration for which the second output is selected to (i) greater than or equal to one-fifth of half the predetermined period and (ii) less than or equal to one-third of half the predetermined period. 
 
     
     
       4. The system of  claim 1 , further comprising:
 a pulse width modulation controller configured to generate the pulse width modulation pulses; and 
 a multiplexer configured to receive as inputs (i) the first output of the first comparator and (ii) the second output of the second comparator, 
 wherein the current control module is configured generate a control signal to control the multiplexer based on the difference between the estimated current through the load and the desired current through the load, 
 wherein the multiplexer is configured to output (i) the first output of the first comparator or (ii) the second output of the second comparator based on the control signal, and 
 wherein the pulse width modulation controller is configured to turn off the switch based on (i) the first output of the first comparator or (ii) the second output of the second comparator output by the multiplexer. 
 
     
     
       5. The system of  claim 1 , further comprising:
 a bridge rectifier configured to convert an AC voltage into a DC voltage; 
 a transformer configured to couple the DC voltage to the load, wherein the switch is connected in series with a primary winding of the transformer, and wherein the load is connected across a secondary winding of the transformer; 
 a current estimating module configured to determine the estimated current through the load based on the first current through the switch; 
 a pulse width modulation controller configured to generate the pulse width modulation pulses; and 
 a multiplexer configured to receive as inputs (i) the first output of the first comparator and (ii) the second output of the second comparator, 
 wherein the current control module is configured generate a control signal to control the multiplexer based on the difference between the estimated current through the load and the desired current through the load, 
 wherein the multiplexer is configured to output (i) the first output of the first comparator or (ii) the second output of the second comparator based on the control signal, and 
 wherein the pulse width modulation controller is configured to turn off the switch based on (i) the first output of the first comparator or (ii) the second output of the second comparator output by the multiplexer. 
 
     
     
       6. The system of  claim 1 , wherein in response to the estimated current through the load being less than the desired current through the load, based on difference between the estimated current through the load and the desired current through the load, the current control module is configured to:
 increase the duration for which the second output is selected, and 
 turn off the switch when the first current through the switch becomes greater than or equal to the second threshold and not when the first current through the switch becomes greater than or equal to the first threshold. 
 
     
     
       7. The system of  claim 1 , wherein in response to the estimated current through the load being greater than the desired current through the load, based on difference between the estimated current through the load and the desired current through the load, the current control module is configured to:
 decrease the duration for which the second output is selected, and 
 turn off the switch when the first current through the switch becomes greater than or equal to the second threshold. 
 
     
     
       8. A method comprising:
 supplying power to a load through a switch in response to the switch being turned on by pulse width modulation pulses; 
 comparing a first current through the switch to a first threshold and generating a first output in response to the first current being greater than or equal to the first threshold; 
 comparing the first current through the switch to a second threshold and generating a second output in response to the first current being greater than or equal to the second threshold, wherein the second threshold is greater than the first threshold; 
 determining an estimated current through the load based on the first current through the switch; 
 select the first output or the second output, 
 turning off the switch based on the first output or the second output; and 
 adjusting a duration for which the second output is selected based on a difference between the estimated current through the load and a desired current through the load. 
 
     
     
       9. The method of  claim 8 , further comprising:
 generating the power based on an AC voltage; and 
 preventing variation of a second current through the load due to an imbalance in the AC voltage by adjusting the duration for which the second output is selected. 
 
     
     
       10. The method of  claim 8 , further comprising:
 generating the power based on an AC voltage having a predetermined period; and 
 reducing a total harmonic distortion in a second current through the load by limiting the duration for which the second output is selected to (i) greater than or equal to one-fifth of half the predetermined period and (ii) less than or equal to one-third of half the predetermined period. 
 
     
     
       11. The method of  claim 8 , further comprising:
 converting an AC voltage into a DC voltage; 
 coupling the DC voltage to the load by a transformer; 
 connecting the switch in series with a primary winding of the transformer; 
 connecting the load across a secondary winding of the transformer; 
 determining the estimated current through the load based on the first current through the switch; and 
 generating the pulse width modulation pulses.